I'm sorry, I don't have anything on this one. The problem for me is that I mainly use perl for web-based code, and C for most of the hard-core, or underside code. Your application specifically requires PHP.
That said, there must be a lot of these kinds of utilities out there in PHP. Have you tried HotScripts?
Not having done anything "real" in AJAX also means my opinion about it should be taken as what it is: hear-say.
Sorry I couldn't be of more help.